During World War II, the BCP actively opposed Bulgaria's Axis alliance by forming partisan terrorist and sabotage groups. In 1942 the broad Fatherland Front coalition was formed as the communists attempted to involve legal opposition groups in exerting antiwar pressure on the government. The coalition's activities brought severe government reprisals. By 1944 partisan units also were being formed in the Bulgarian army.

The Red Army invasion of September 1944 found a temporary Bulgarian government desperately trying to avoid accommodation with the communist left or the pro-German right, but under intense diplomatic and military pressure from both Germany and the Soviet Union. Boris had died in 1943 and by 1944 severe wartime shortages (partly caused by peasants hoarding food supplies) eroded support for the government.

When Soviet troops entered Bulgaria, the Fatherland Front engineered a bloodless coup displacing the government of Prime Minister Konstantin Muraviev. In 1946 the first Fatherland Front government divided ministries among the BCP, Zveno, the Bulgarian Agrarian National Union (BANU), and the Bulgarian Social Democratic Party (BSDP). Within a year, the BCP had used that power base to purge the government of all key opposition figures and dominate the Fatherland Front. In 1946 a national referendum rejected the monarchy in favor of a people's republic, leading to the immediate exile of Simeon II, nine-year-old son of Boris III. The following month, the communists easily won a national election for representatives to a subranie to write a new constitution over the objections of BANU, which sought a return to the Turnovo Constitution. In early 1947, the conclusion of peace between Bulgaria and the Allies eliminated the Allied Control Commission, through which Britain had maintained some influence on domestic Bulgarian politics. By that time, the only remaining obstacle to total BCP domination was Nikola Petkov's BANU, in a coalition with other noncommunist parties. The power struggle ended abruptly in mid-1947, when the Fatherland Front arrested and executed Petkov as a Western agent. This event paved the way for unanimous adoption of a new constitution in December 1947. The new document was closely modeled on the 1936 Soviet constitution.

The parliamentary election of fall 1946 gave the BCP 275 of 465 seats and made Georgi Dimitrov prime minister. The communists gained control of all significant ministries, beginning the last stage of consolidating communist dictatorship. The ensuing regimes of Dimitrov and Chervenkov defined Bulgaria as a highly conventional communist state and isolated it from nearly all noncommunist commercial and cultural influences.

Data as of June 1992